Herbicide Formulations

Abstract

Background: Herbicides comprise nearly half of the 5 billion pounds of pesticide active ingredients used worldwide annually. The active ingredient must be formulated with other ingredients to allow mixing, dilution, application, and stability. Liquid commercial formulations for spray foliar application include water-soluble liquids, emulsifiable concentrates, suspension concentrates or “flowables,” and gels. Dry formulations that are mixed with water for spray application include wettable powders and water-dispersible granules. Granules are broadcast directly out of the bag. The carrier in liquid formulations is either water or an organic solvent or oil. The general chemical class of the carrier may be deduced based on the solubility characteristics of the active ingredient. Cosolvents may be necessary to optimize solubility and stability. Surfactants are nearly universally present in herbicide formulations or added prior to application. They aid uniform spreading of the spray droplet on the leaf and penetration of its waxy cuticle by the active ingredient. In solvent-based formulations, surfactants permit a stable oil-in-water emulsion to form when diluted with water for actual use. New surfactant systems are currently of intense competitive importance. Other formulation ingredients include pH adjusters, buffers, milling aids, antifoaming agents, acid scavengers, dyes, suspending agents, preservatives, dispersants, emulsifiers, densifiers, antifreeze, and crystal promoters. In highly regulated environments, the other formulation components in pesticides are receiving scrutiny. In the US, the EPA's strategy has been to categorize currently used formulation ingredients into 4 lists based on their toxicology profiles. The ultimate outcome is to have all inert ingredients on List 4, Minimal Risk. List 4 ingredients are generally regarded as safe or have current use patterns that do not pose an unreasonable risk of adverse effect to public health or the environment.